Development and studies of a time projection chamber with GEMs

Future high-energy physics experiments will have stringent requirements on the quality of their central tracking systems. In order to evaluate whether a Time Projection Chamber (TPC) in combination with a Micro-Pattern Gas Amplification stage can meet these demands, a small cylindrical prototype has been equipped with two Gas Electron Multipliers (OEMs) and micropads connected to highly integrated front-end electronics. In earlier tests with this system in high-rate particle beams - but without magnetic field - at the Proton-Synchrotron at CERN, high efficiencies and good single-pad-row spatial resolutions could be demonstrated. We now present complementary measurements with this system in high magnetic fields up to 5 T at DESY (Hamburg, Germany). Detailed results are given for the spatial resolution dependence on parameters such as drift distance, effective gas gain and magnetic field. Transverse single- pad-row spatial resolution was found to be as low as (53 plus or minus 5) urn and a previously published model for the extrapolation of the beam test resulting in large scale operation conditions at the Linear Collider could be confirmed.